That most vivid of rites of early summer, when Rafael Nadal launches his whirling, technicolour assault on the French Open, is upon us with the year's second grand slam starting today.

It is hard to overstate what a boon the Spaniard has been to the clay-court game - and what a transformation he has brought to our image of how his countrymen play on the carpet of crushed house brick that is freshly spread each spring over the courts of Roland Garros.

For years, the Spanish took so literally the idea that the clay-court game is tennis's version of chess that they might more appropriately have worn suits to give their intensely studious performances. Now we have Garry Kasparov in streetwear and the prospect of Nadal's all-action defence of his record of never having lost at the French Open is as tantalising as any sporting treat this summer.

Remember the 2002 French final when Albert Costa beat Juan Carlos Ferrero, or 1994 when Sergi Bruguera beat Alberto Berasategui, whose extreme, restricting grip was such that he hit forehands and backhands with the same side of the racket (and that was as interesting as he got)? The chances are these matches passed you by in a blur of tedium.

In their place we have Nadal, and he deserves our deepest thanks. The Majorcan has won all 21 of his matches at Roland Garros, to claim the past three French titles in such vibrant style that we are passing through what will almost certainly be remembered as a grande époque in the tournament's history.

Last Sunday, Nadal achieved his 21st clay-court triumph in 22 tournaments by beating Roger Federer in an outstanding final in Hamburg. One Spanish newspaper ran its report of the match under a headline that read simply 'Nadalísimo'. Manolo Santana, who won two French titles in the 1960s and is the only Spaniard to have won Wimbledon, in 1966, said after this latest win over Federer that he now regarded Nadal as the greatest clay-court player ever.

Hamburg was the one big title missing from Nadal's clay-court record and it was a hugely significant win in the context of his rivalry with Federer, the world's number one for the past four years. The court at the Rothenbaum stadium is markedly slower than Roland Garros and this gives Federer an improved chance of beating Nadal, but the Spaniard was still able to impose himself.

Andy Murray, who had an uncomfortable close-up view of Nadal in Hamburg 10 days ago, when he lost to him in straight sets on his 21st birthday, explains why Federer will find it harder against Nadal if they do meet again in a fortnight in the French final. 'At the French, the balls are quick and the courts are fast and Nadal's forehand is bouncing into the front row of the stands. To have to keep hitting from up here is so tiring,' Murray says, playing an imaginary return from shoulder level.

Murray has always been a keen analyst - his mother recalls being regaled by her son, when he was small, with a detailed account of what the loser had done wrong in a match they watched together - and after he left Hamburg he switched on the TV in London to study Nadal's technique. He says it was only then that he appreciated one of the key elements of Nadal's success on clay: his ability to slide on either foot.

Sliding, rather than running, into shots is as fundamental to being accomplished at clay-court tennis as jumping is to being a good attacker in basketball. To slide well, a player really needs to have been doing it from a young age, and even then most players stick to being left or right-footed sliders. Nadal is that rarity who can do it on either side. 'It makes a big difference and gives him a huge advantage over anyone he plays,' Murray says. 'It's so much easier to be balanced on the right balls for passing shots and also to recover after playing these shots.'

Murray thinks if Federer were able to maintain his very best form on clay throughout a match he would beat Nadal and win his first French Open, but he does not expect this to happen - not this year, at least. 'Nadal plays like this,' Murray says, and again raises an arm up high, this time to draw a flat, horizontal line. 'He maintains his form pretty much throughout the match, but Federer on clay is a little bit up and down and this makes it difficult for him. He's pushed him close so many times, but Nadal always comes back.'

Of his own chances, Murray says he is ambivalent about playing on clay, describing it as 'my favourite surface to play on but not necessarily my best to win matches on'. He says his ambition, is to reach the second week in this, the only grand slam in which he has never won a match, something he should put right against the French teenager Jonathan Eysseric in the first round. He talks about the number of unseeded players 'who can go on runs' and says: 'Hopefully I'll avoid them and draw some Americans.'

This dig is unlikely to come back to haunt him. For a start no American is near him in the draw, and the collective lack of will that the US contingent have shown for what they dismissively call 'dirt-ball tennis' has been all too evident in recent years. Andy Roddick has already pulled out and the rest are likely to be pushed out early on by the clay-loving Europeans and South Americans.

Like most of the rest of us, Murray is not looking beyond the world's top three - Federer, Nadal and Novak Djokovic - for the 2008 champion. Djokovic, the winner of the year's first grand slam, January's Australian Open in Melbourne, undoubtedly has the ability to break the duopoly that Federer and Nadal have imposed on the men's singles final in Paris for the past two years. What is less likely is that he quite has the fortitude to come out on top, particularly against Nadal, whose title defences are waged, increasingly, with a feral tenacity.

A year ago, Nadal beat Djokovic in the semi-finals, the score of 7-5 6-4 6-2 indicating the slow, brutal crushing of the Serb's spirit. 'To win against him on clay, you've got to do more than on other surfaces,' Djokovic said, forlornly. 'You've got to push him more, push him over the limit. You've got to play really great tennis, and it has got to be your day.'

It is not only the way he plays that makes Nadal so formidable, but the way he deals with the physical and mental stresses. Although his feet are protected by special shoes, made to withstand his constant percussive movement - very different from Federer's soft-shoe shuffle - he will take a badly blistered right foot into this year's championships and a left shoulder that is prone to tendinitis. These just add to the mental pressure of staying at the top, with which Nadal deals so stoically.

If he were to pull it off, he would become only the second player after Bjorn Borg, whose six titles included an unbroken sequence from 1978 to 1981, to win the French four years in a row. From the Swedish Iceman to the Spanish Firebrand - the contrast could hardly be more marked.